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 $188.99   13.661%   $214.8079   $214.81   $214.80   $214.80  
  Purchase #2 $82.98   6.820%   $88.6392   $88.64   $88.65   $88.60  
  Purchase #3 $169.29   4.518%   $176.9385   $176.94   $176.95   $176.90  
  Purchase #4 $194.41   5.377%   $204.8634   $204.86   $204.85   $204.90  
  Purchase #5 $123.83   13.274%   $140.2672   $140.27   $140.25   $140.30  
  Purchase #6 $189.52   9.427%   $207.3861   $207.39   $207.40   $207.40  
  Purchase #7 $115.79   4.751%   $121.2912   $121.29   $121.30   $121.30  
  7 purchase totals = $1,064.81       $1,154.1935   $1,154.20   $1,154.20   $1,154.20