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 $97.29   9.678%   $106.7057   $106.71   $106.70   $106.70  
  Purchase #2 $119.44   6.179%   $126.8202   $126.82   $126.80   $126.80  
  Purchase #3 $55.50   3.292%   $57.3271   $57.33   $57.35   $57.30  
  Purchase #4 $135.76   4.343%   $141.6561   $141.66   $141.65   $141.70  
  Purchase #5 $197.84   5.301%   $208.3275   $208.33   $208.35   $208.30  
  Purchase #6 $245.69   4.345%   $256.3652   $256.37   $256.35   $256.40  
  Purchase #7 $117.43   10.500%   $129.7602   $129.76   $129.75   $129.80  
  7 purchase totals = $968.95       $1,026.9620   $1,026.98   $1,026.95   $1,027.00