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 $89.68   7.150%   $96.0921   $96.09   $96.10   $96.10  
  Purchase #2 $32.33   9.864%   $35.519   $35.52   $35.50   $35.50  
  Purchase #3 $201.64   12.198%   $226.236   $226.24   $226.25   $226.20  
  Purchase #4 $85.65   11.267%   $95.3002   $95.30   $95.30   $95.30  
  Purchase #5 $10.27   13.713%   $11.6783   $11.68   $11.70   $11.70  
  Purchase #6 $250.80   5.265%   $264.0046   $264.00   $264.00   $264.00  
  Purchase #7 $38.94   5.675%   $41.1498   $41.15   $41.15   $41.10  
  7 purchase totals = $709.31       $769.9800   $769.98   $770.00   $769.90