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 $166.85   12.522%   $187.743   $187.74   $187.75   $187.70  
  Purchase #2 $59.78   13.794%   $68.0261   $68.03   $68.05   $68.00  
  Purchase #3 $193.79   3.604%   $200.7742   $200.77   $200.75   $200.80  
  Purchase #4 $227.56   11.780%   $254.3666   $254.37   $254.35   $254.40  
  Purchase #5 $95.59   5.233%   $100.5922   $100.59   $100.60   $100.60  
  Purchase #6 $165.95   5.408%   $174.9246   $174.92   $174.90   $174.90  
  Purchase #7 $243.59   13.834%   $277.2882   $277.29   $277.30   $277.30  
  7 purchase totals = $1,153.11       $1,263.7149   $1,263.71   $1,263.70   $1,263.70