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 $62.89   13.335%   $71.2764   $71.28   $71.30   $71.30  
  Purchase #2 $242.51   10.239%   $267.3406   $267.34   $267.35   $267.30  
  Purchase #3 $205.57   5.582%   $217.0449   $217.04   $217.05   $217.00  
  Purchase #4 $131.27   5.775%   $138.8508   $138.85   $138.85   $138.90  
  Purchase #5 $122.79   10.839%   $136.0992   $136.10   $136.10   $136.10  
  Purchase #6 $110.53   12.469%   $124.312   $124.31   $124.30   $124.30  
  Purchase #7 $87.59   4.646%   $91.6594   $91.66   $91.65   $91.70  
  7 purchase totals = $963.15       $1,046.5833   $1,046.58   $1,046.60   $1,046.60