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 $174.44   5.677%   $184.343   $184.34   $184.35   $184.30  
  Purchase #2 $78.95   6.192%   $83.8386   $83.84   $83.85   $83.80  
  Purchase #3 $44.53   6.410%   $47.3844   $47.38   $47.40   $47.40  
  Purchase #4 $126.55   10.501%   $139.839   $139.84   $139.85   $139.80  
  Purchase #5 $79.28   9.757%   $87.0153   $87.02   $87.00   $87.00  
  Purchase #6 $200.62   8.205%   $217.0809   $217.08   $217.10   $217.10  
  Purchase #7 $88.38   4.730%   $92.5604   $92.56   $92.55   $92.60  
  7 purchase totals = $792.75       $852.0616   $852.06   $852.10   $852.00