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 $60.96   4.715%   $63.8343   $63.83   $63.85   $63.80  
  Purchase #2 $193.95   8.867%   $211.1475   $211.15   $211.15   $211.10  
  Purchase #3 $164.39   13.232%   $186.1421   $186.14   $186.15   $186.10  
  Purchase #4 $128.98   4.418%   $134.6783   $134.68   $134.70   $134.70  
  Purchase #5 $220.52   13.503%   $250.2968   $250.30   $250.30   $250.30  
  Purchase #6 $32.80   9.725%   $35.9898   $35.99   $36.00   $36.00  
  Purchase #7 $126.43   11.288%   $140.7014   $140.70   $140.70   $140.70  
  7 purchase totals = $928.03       $1,022.7902   $1,022.79   $1,022.85   $1,022.70