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 $235.56   6.868%   $251.7383   $251.74   $251.75   $251.70  
  Purchase #2 $109.82   7.180%   $117.7051   $117.71   $117.70   $117.70  
  Purchase #3 $153.44   7.404%   $164.8007   $164.80   $164.80   $164.80  
  Purchase #4 $32.31   5.710%   $34.1549   $34.15   $34.15   $34.20  
  Purchase #5 $92.84   11.809%   $103.8035   $103.80   $103.80   $103.80  
  Purchase #6 $73.40   9.816%   $80.6049   $80.60   $80.60   $80.60  
  Purchase #7 $162.52   6.706%   $173.4186   $173.42   $173.40   $173.40  
  7 purchase totals = $859.89       $926.2260   $926.22   $926.20   $926.20