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 $153.82   4.208%   $160.2927   $160.29   $160.30   $160.30  
  Purchase #2 $108.41   13.279%   $122.8058   $122.81   $122.80   $122.80  
  Purchase #3 $235.54   7.310%   $252.758   $252.76   $252.75   $252.80  
  Purchase #4 $204.32   3.234%   $210.9277   $210.93   $210.95   $210.90  
  Purchase #5 $153.71   4.649%   $160.856   $160.86   $160.85   $160.90  
  Purchase #6 $111.96   3.445%   $115.817   $115.82   $115.80   $115.80  
  Purchase #7 $212.71   13.173%   $240.7303   $240.73   $240.75   $240.70  
  7 purchase totals = $1,180.47       $1,264.1875   $1,264.20   $1,264.20   $1,264.20