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 $23.52   13.831%   $26.7731   $26.77   $26.75   $26.80  
  Purchase #2 $30.43   13.753%   $34.615   $34.62   $34.60   $34.60  
  Purchase #3 $246.98   3.415%   $255.4144   $255.41   $255.40   $255.40  
  Purchase #4 $65.52   13.739%   $74.5218   $74.52   $74.50   $74.50  
  Purchase #5 $63.94   3.119%   $65.9343   $65.93   $65.95   $65.90  
  Purchase #6 $185.88   6.222%   $197.4455   $197.45   $197.45   $197.40  
  Purchase #7 $171.27   4.846%   $179.5697   $179.57   $179.55   $179.60  
  7 purchase totals = $787.54       $834.2738   $834.27   $834.20   $834.20