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 $232.62   8.124%   $251.518   $251.52   $251.50   $251.50  
  Purchase #2 $197.97   10.591%   $218.937   $218.94   $218.95   $218.90  
  Purchase #3 $50.37   6.580%   $53.6843   $53.68   $53.70   $53.70  
  Purchase #4 $233.31   3.560%   $241.6158   $241.62   $241.60   $241.60  
  Purchase #5 $106.27   8.289%   $115.0787   $115.08   $115.10   $115.10  
  Purchase #6 $59.85   3.798%   $62.1231   $62.12   $62.10   $62.10  
  Purchase #7 $117.77   10.325%   $129.9298   $129.93   $129.95   $129.90  
  7 purchase totals = $998.16       $1,072.8867   $1,072.89   $1,072.90   $1,072.80