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 $63.85   9.607%   $69.9841   $69.98   $70.00   $70.00  
  Purchase #2 $44.61   6.148%   $47.3526   $47.35   $47.35   $47.40  
  Purchase #3 $190.41   5.346%   $200.5893   $200.59   $200.60   $200.60  
  Purchase #4 $183.84   9.623%   $201.5309   $201.53   $201.55   $201.50  
  Purchase #5 $177.48   9.733%   $194.7541   $194.75   $194.75   $194.80  
  Purchase #6 $106.79   12.103%   $119.7148   $119.71   $119.70   $119.70  
  Purchase #7 $182.59   12.248%   $204.9536   $204.95   $204.95   $205.00  
  7 purchase totals = $949.57       $1,038.8794   $1,038.86   $1,038.90   $1,039.00