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 $89.76   13.260%   $101.6622   $101.66   $101.65   $101.70  
  Purchase #2 $208.79   8.682%   $226.9171   $226.92   $226.90   $226.90  
  Purchase #3 $49.77   10.235%   $54.864   $54.86   $54.85   $54.90  
  Purchase #4 $243.84   6.761%   $260.326   $260.33   $260.35   $260.30  
  Purchase #5 $155.36   12.726%   $175.1311   $175.13   $175.15   $175.10  
  Purchase #6 $63.36   8.723%   $68.8869   $68.89   $68.90   $68.90  
  Purchase #7 $245.58   8.331%   $266.0393   $266.04   $266.05   $266.00  
  7 purchase totals = $1,056.46       $1,153.8266   $1,153.83   $1,153.85   $1,153.80