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 $224.80   3.799%   $233.3402   $233.34   $233.35   $233.30  
  Purchase #2 $180.97   10.669%   $200.2777   $200.28   $200.30   $200.30  
  Purchase #3 $246.33   6.191%   $261.5803   $261.58   $261.60   $261.60  
  Purchase #4 $27.73   3.481%   $28.6953   $28.70   $28.70   $28.70  
  Purchase #5 $117.32   5.668%   $123.9697   $123.97   $123.95   $124.00  
  Purchase #6 $150.60   12.335%   $169.1765   $169.18   $169.20   $169.20  
  Purchase #7 $49.33   9.529%   $54.0307   $54.03   $54.05   $54.00  
  7 purchase totals = $997.08       $1,071.0704   $1,071.08   $1,071.15   $1,071.10