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 $7.90   5.166%   $8.3081   $8.31   $8.30   $8.30  
  Purchase #2 $178.78   8.803%   $194.518   $194.52   $194.50   $194.50  
  Purchase #3 $159.51   13.547%   $181.1188   $181.12   $181.10   $181.10  
  Purchase #4 $77.70   5.155%   $81.7054   $81.71   $81.70   $81.70  
  Purchase #5 $173.85   5.134%   $182.7755   $182.78   $182.80   $182.80  
  Purchase #6 $237.95   3.396%   $246.0308   $246.03   $246.05   $246.00  
  Purchase #7 $176.71   9.119%   $192.8242   $192.82   $192.80   $192.80  
  7 purchase totals = $1,012.40       $1,087.2808   $1,087.29   $1,087.25   $1,087.20