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 $57.47   12.584%   $64.702   $64.70   $64.70   $64.70  
  Purchase #2 $119.93   8.262%   $129.8386   $129.84   $129.85   $129.80  
  Purchase #3 $147.82   3.285%   $152.6759   $152.68   $152.70   $152.70  
  Purchase #4 $161.62   4.485%   $168.8687   $168.87   $168.85   $168.90  
  Purchase #5 $231.41   9.776%   $254.0326   $254.03   $254.05   $254.00  
  Purchase #6 $202.70   8.769%   $220.4748   $220.47   $220.45   $220.50  
  Purchase #7 $191.65   10.492%   $211.7579   $211.76   $211.75   $211.80  
  7 purchase totals = $1,112.60       $1,202.3505   $1,202.35   $1,202.35   $1,202.40