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 $216.50   6.461%   $230.4881   $230.49   $230.50   $230.50  
  Purchase #2 $48.69   11.537%   $54.3074   $54.31   $54.30   $54.30  
  Purchase #3 $108.27   9.795%   $118.875   $118.88   $118.90   $118.90  
  Purchase #4 $220.85   5.179%   $232.2878   $232.29   $232.30   $232.30  
  Purchase #5 $38.29   7.345%   $41.1024   $41.10   $41.10   $41.10  
  Purchase #6 $117.27   6.821%   $125.269   $125.27   $125.25   $125.30  
  Purchase #7 $211.64   11.517%   $236.0146   $236.01   $236.00   $236.00  
  7 purchase totals = $961.51       $1,038.3443   $1,038.35   $1,038.35   $1,038.40