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 $225.40   3.819%   $234.008   $234.01   $234.00   $234.00  
  Purchase #2 $9.69   9.137%   $10.5754   $10.58   $10.60   $10.60  
  Purchase #3 $8.80   10.200%   $9.6976   $9.70   $9.70   $9.70  
  Purchase #4 $78.84   12.762%   $88.9016   $88.90   $88.90   $88.90  
  Purchase #5 $206.77   12.532%   $232.6824   $232.68   $232.70   $232.70  
  Purchase #6 $61.38   7.164%   $65.7773   $65.78   $65.80   $65.80  
  Purchase #7 $105.79   13.506%   $120.078   $120.08   $120.10   $120.10  
  7 purchase totals = $696.67       $761.7203   $761.73   $761.80   $761.80