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 $49.53   7.865%   $53.4255   $53.43   $53.45   $53.40  
  Purchase #2 $156.56   5.129%   $164.59   $164.59   $164.60   $164.60  
  Purchase #3 $207.84   5.503%   $219.2774   $219.28   $219.30   $219.30  
  Purchase #4 $48.77   5.323%   $51.366   $51.37   $51.35   $51.40  
  Purchase #5 $179.55   13.717%   $204.1789   $204.18   $204.20   $204.20  
  Purchase #6 $237.57   3.529%   $245.9538   $245.95   $245.95   $246.00  
  Purchase #7 $200.38   9.854%   $220.1254   $220.13   $220.15   $220.10  
  7 purchase totals = $1,080.20       $1,158.9170   $1,158.93   $1,159.00   $1,159.00