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 $168.80   3.537%   $174.7705   $174.77   $174.75   $174.80  
  Purchase #2 $62.32   11.471%   $69.4687   $69.47   $69.45   $69.50  
  Purchase #3 $195.53   3.401%   $202.18   $202.18   $202.20   $202.20  
  Purchase #4 $246.99   11.719%   $275.9348   $275.93   $275.95   $275.90  
  Purchase #5 $16.42   4.842%   $17.2151   $17.22   $17.20   $17.20  
  Purchase #6 $249.52   3.132%   $257.335   $257.34   $257.35   $257.30  
  Purchase #7 $228.34   9.330%   $249.6441   $249.64   $249.65   $249.60  
  7 purchase totals = $1,167.92       $1,246.5482   $1,246.55   $1,246.55   $1,246.50