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 $97.58   5.751%   $103.1918   $103.19   $103.20   $103.20  
  Purchase #2 $138.60   12.832%   $156.3852   $156.39   $156.40   $156.40  
  Purchase #3 $210.38   12.582%   $236.85   $236.85   $236.85   $236.90  
  Purchase #4 $55.51   4.651%   $58.0918   $58.09   $58.10   $58.10  
  Purchase #5 $219.99   5.442%   $231.9619   $231.96   $231.95   $232.00  
  Purchase #6 $187.28   13.473%   $212.5122   $212.51   $212.50   $212.50  
  Purchase #7 $54.42   12.738%   $61.352   $61.35   $61.35   $61.40  
  7 purchase totals = $963.76       $1,060.3449   $1,060.34   $1,060.35   $1,060.50