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 $235.37   11.690%   $262.8848   $262.88   $262.90   $262.90  
  Purchase #2 $83.26   6.405%   $88.5928   $88.59   $88.60   $88.60  
  Purchase #3 $176.98   13.213%   $200.3644   $200.36   $200.35   $200.40  
  Purchase #4 $62.71   4.148%   $65.3112   $65.31   $65.30   $65.30  
  Purchase #5 $151.71   5.262%   $159.693   $159.69   $159.70   $159.70  
  Purchase #6 $181.61   5.557%   $191.7021   $191.70   $191.70   $191.70  
  Purchase #7 $201.98   13.303%   $228.8494   $228.85   $228.85   $228.80  
  7 purchase totals = $1,093.62       $1,197.3977   $1,197.38   $1,197.40   $1,197.40