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 $64.95   12.237%   $72.8979   $72.90   $72.90   $72.90  
  Purchase #2 $101.96   8.525%   $110.6521   $110.65   $110.65   $110.70  
  Purchase #3 $68.77   11.870%   $76.933   $76.93   $76.95   $76.90  
  Purchase #4 $94.74   12.723%   $106.7938   $106.79   $106.80   $106.80  
  Purchase #5 $148.75   4.122%   $154.8815   $154.88   $154.90   $154.90  
  Purchase #6 $58.87   5.184%   $61.9218   $61.92   $61.90   $61.90  
  Purchase #7 $186.52   8.840%   $203.0084   $203.01   $203.00   $203.00  
  7 purchase totals = $724.56       $787.0885   $787.08   $787.10   $787.10