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 $51.93   7.769%   $55.9644   $55.96   $55.95   $56.00  
  Purchase #2 $81.47   8.582%   $88.4618   $88.46   $88.45   $88.50  
  Purchase #3 $226.39   13.645%   $257.2809   $257.28   $257.30   $257.30  
  Purchase #4 $113.57   6.415%   $120.8555   $120.86   $120.85   $120.90  
  Purchase #5 $202.76   12.455%   $228.0138   $228.01   $228.00   $228.00  
  Purchase #6 $173.62   11.252%   $193.1557   $193.16   $193.15   $193.20  
  Purchase #7 $61.38   11.752%   $68.5934   $68.59   $68.60   $68.60  
  7 purchase totals = $911.12       $1,012.3255   $1,012.32   $1,012.30   $1,012.50