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 $250.92   4.644%   $262.5727   $262.57   $262.55   $262.60  
  Purchase #2 $85.72   13.871%   $97.6102   $97.61   $97.60   $97.60  
  Purchase #3 $153.70   8.250%   $166.3803   $166.38   $166.40   $166.40  
  Purchase #4 $207.77   6.289%   $220.8367   $220.84   $220.85   $220.80  
  Purchase #5 $65.84   5.221%   $69.2775   $69.28   $69.30   $69.30  
  Purchase #6 $130.30   13.566%   $147.9765   $147.98   $148.00   $148.00  
  Purchase #7 $60.73   8.231%   $65.7287   $65.73   $65.75   $65.70  
  7 purchase totals = $954.98       $1,030.3826   $1,030.39   $1,030.45   $1,030.40