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 $48.29   13.319%   $54.7217   $54.72   $54.70   $54.70  
  Purchase #2 $150.78   10.385%   $166.4385   $166.44   $166.45   $166.40  
  Purchase #3 $111.31   6.414%   $118.4494   $118.45   $118.45   $118.40  
  Purchase #4 $231.91   11.553%   $258.7026   $258.70   $258.70   $258.70  
  Purchase #5 $228.46   9.644%   $250.4927   $250.49   $250.50   $250.50  
  Purchase #6 $77.68   12.753%   $87.5865   $87.59   $87.60   $87.60  
  Purchase #7 $250.72   6.191%   $266.2421   $266.24   $266.25   $266.20  
  7 purchase totals = $1,099.15       $1,202.6335   $1,202.63   $1,202.65   $1,202.50