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 $65.98   4.837%   $69.1715   $69.17   $69.15   $69.20  
  Purchase #2 $43.37   7.802%   $46.7537   $46.75   $46.75   $46.80  
  Purchase #3 $216.95   5.130%   $228.0795   $228.08   $228.10   $228.10  
  Purchase #4 $167.48   11.342%   $186.4756   $186.48   $186.50   $186.50  
  Purchase #5 $43.62   7.242%   $46.779   $46.78   $46.80   $46.80  
  Purchase #6 $187.69   7.436%   $201.6466   $201.65   $201.65   $201.60  
  Purchase #7 $48.40   8.372%   $52.452   $52.45   $52.45   $52.50  
  7 purchase totals = $773.49       $831.3579   $831.36   $831.40   $831.50