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 $41.62   6.714%   $44.4144   $44.41   $44.40   $44.40  
  Purchase #2 $137.41   10.268%   $151.5193   $151.52   $151.50   $151.50  
  Purchase #3 $172.36   6.474%   $183.5186   $183.52   $183.50   $183.50  
  Purchase #4 $139.72   10.103%   $153.8359   $153.84   $153.85   $153.80  
  Purchase #5 $97.61   3.498%   $101.0244   $101.02   $101.00   $101.00  
  Purchase #6 $202.50   8.857%   $220.4354   $220.44   $220.45   $220.40  
  Purchase #7 $238.97   3.279%   $246.8058   $246.81   $246.80   $246.80  
  7 purchase totals = $1,030.19       $1,101.5538   $1,101.56   $1,101.50   $1,101.40