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 $187.58   10.492%   $207.2609   $207.26   $207.25   $207.30  
  Purchase #2 $179.73   3.364%   $185.7761   $185.78   $185.80   $185.80  
  Purchase #3 $103.68   7.481%   $111.4363   $111.44   $111.45   $111.40  
  Purchase #4 $80.66   8.285%   $87.3427   $87.34   $87.35   $87.30  
  Purchase #5 $16.26   11.355%   $18.1063   $18.11   $18.10   $18.10  
  Purchase #6 $125.95   8.282%   $136.3812   $136.38   $136.40   $136.40  
  Purchase #7 $53.64   12.256%   $60.2141   $60.21   $60.20   $60.20  
  7 purchase totals = $747.50       $806.5176   $806.52   $806.55   $806.50