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 $96.28   5.432%   $101.5099   $101.51   $101.50   $101.50  
  Purchase #2 $210.77   12.285%   $236.6631   $236.66   $236.65   $236.70  
  Purchase #3 $45.57   9.266%   $49.7925   $49.79   $49.80   $49.80  
  Purchase #4 $21.76   13.280%   $24.6497   $24.65   $24.65   $24.60  
  Purchase #5 $96.40   5.814%   $102.0047   $102.00   $102.00   $102.00  
  Purchase #6 $147.61   11.301%   $164.2914   $164.29   $164.30   $164.30  
  Purchase #7 $247.56   12.620%   $278.8021   $278.80   $278.80   $278.80  
  7 purchase totals = $865.95       $957.7134   $957.70   $957.70   $957.70