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 $58.79   11.746%   $65.6955   $65.70   $65.70   $65.70  
  Purchase #2 $179.97   8.433%   $195.1469   $195.15   $195.15   $195.10  
  Purchase #3 $76.65   5.387%   $80.7791   $80.78   $80.80   $80.80  
  Purchase #4 $231.68   8.346%   $251.016   $251.02   $251.00   $251.00  
  Purchase #5 $155.84   13.362%   $176.6633   $176.66   $176.65   $176.70  
  Purchase #6 $80.91   9.483%   $88.5827   $88.58   $88.60   $88.60  
  Purchase #7 $161.86   12.712%   $182.4356   $182.44   $182.45   $182.40  
  7 purchase totals = $945.70       $1,040.3191   $1,040.33   $1,040.35   $1,040.30