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 $77.57   13.481%   $88.0272   $88.03   $88.05   $88.00  
  Purchase #2 $196.53   3.131%   $202.6834   $202.68   $202.70   $202.70  
  Purchase #3 $194.34   3.402%   $200.9514   $200.95   $200.95   $201.00  
  Purchase #4 $48.94   6.148%   $51.9488   $51.95   $51.95   $51.90  
  Purchase #5 $212.39   3.220%   $219.229   $219.23   $219.25   $219.20  
  Purchase #6 $237.30   12.198%   $266.2459   $266.25   $266.25   $266.20  
  Purchase #7 $114.98   5.571%   $121.3855   $121.39   $121.40   $121.40  
  7 purchase totals = $1,082.05       $1,150.4712   $1,150.48   $1,150.55   $1,150.40