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 $111.78   8.446%   $121.2209   $121.22   $121.20   $121.20  
  Purchase #2 $230.88   6.789%   $246.5544   $246.55   $246.55   $246.60  
  Purchase #3 $223.35   11.316%   $248.6243   $248.62   $248.60   $248.60  
  Purchase #4 $238.78   7.740%   $257.2616   $257.26   $257.25   $257.30  
  Purchase #5 $205.29   12.308%   $230.5571   $230.56   $230.55   $230.60  
  Purchase #6 $51.27   5.706%   $54.1955   $54.20   $54.20   $54.20  
  Purchase #7 $95.27   8.415%   $103.287   $103.29   $103.30   $103.30  
  7 purchase totals = $1,156.62       $1,261.7008   $1,261.70   $1,261.65   $1,261.80