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 $100.78   9.861%   $110.7179   $110.72   $110.70   $110.70  
  Purchase #2 $65.79   13.792%   $74.8638   $74.86   $74.85   $74.90  
  Purchase #3 $102.36   12.786%   $115.4477   $115.45   $115.45   $115.40  
  Purchase #4 $9.33   5.802%   $9.8713   $9.87   $9.85   $9.90  
  Purchase #5 $145.84   11.819%   $163.0768   $163.08   $163.10   $163.10  
  Purchase #6 $8.37   9.361%   $9.1535   $9.15   $9.15   $9.20  
  Purchase #7 $80.96   11.237%   $90.0575   $90.06   $90.05   $90.10  
  7 purchase totals = $513.43       $573.1885   $573.19   $573.15   $573.30