Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.70   12.254%   $207.3331   $207.33   $207.35   $207.30  
  Purchase #2 $241.91   11.474%   $269.6668   $269.67   $269.65   $269.70  
  Purchase #3 $246.47   5.801%   $260.7677   $260.77   $260.75   $260.80  
  Purchase #4 $247.78   12.433%   $278.5865   $278.59   $278.60   $278.60  
  Purchase #5 $153.67   3.598%   $159.199   $159.20   $159.20   $159.20  
  Purchase #6 $110.93   9.155%   $121.0856   $121.09   $121.10   $121.10  
  Purchase #7 $209.29   7.819%   $225.6544   $225.65   $225.65   $225.70  
  7 purchase totals = $1,394.75       $1,522.2931   $1,522.30   $1,522.30   $1,522.40