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 $114.71   6.200%   $121.822   $121.82   $121.80   $121.80  
  Purchase #2 $116.83   5.567%   $123.3339   $123.33   $123.35   $123.30  
  Purchase #3 $58.99   5.476%   $62.2203   $62.22   $62.20   $62.20  
  Purchase #4 $102.82   3.586%   $106.5071   $106.51   $106.50   $106.50  
  Purchase #5 $101.89   6.138%   $108.144   $108.14   $108.15   $108.10  
  Purchase #6 $207.28   7.836%   $223.5225   $223.52   $223.50   $223.50  
  Purchase #7 $212.29   6.590%   $226.2799   $226.28   $226.30   $226.30  
  7 purchase totals = $914.81       $971.8297   $971.82   $971.80   $971.70