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 $77.62   8.302%   $84.064   $84.06   $84.05   $84.10  
  Purchase #2 $202.87   11.238%   $225.6685   $225.67   $225.65   $225.70  
  Purchase #3 $87.40   13.765%   $99.4306   $99.43   $99.45   $99.40  
  Purchase #4 $111.86   12.259%   $125.5729   $125.57   $125.55   $125.60  
  Purchase #5 $167.65   6.253%   $178.1332   $178.13   $178.15   $178.10  
  Purchase #6 $55.41   8.518%   $60.1298   $60.13   $60.15   $60.10  
  Purchase #7 $114.92   6.680%   $122.5967   $122.60   $122.60   $122.60  
  7 purchase totals = $817.73       $895.5957   $895.59   $895.60   $895.60