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 $246.80   9.801%   $270.9889   $270.99   $271.00   $271.00  
  Purchase #2 $168.45   3.483%   $174.3171   $174.32   $174.30   $174.30  
  Purchase #3 $249.96   11.234%   $278.0405   $278.04   $278.05   $278.00  
  Purchase #4 $59.56   11.117%   $66.1813   $66.18   $66.20   $66.20  
  Purchase #5 $93.78   6.315%   $99.7022   $99.70   $99.70   $99.70  
  Purchase #6 $140.67   9.182%   $153.5863   $153.59   $153.60   $153.60  
  Purchase #7 $211.34   9.567%   $231.5589   $231.56   $231.55   $231.60  
  7 purchase totals = $1,170.56       $1,274.3752   $1,274.38   $1,274.40   $1,274.40