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 $219.66   7.750%   $236.6837   $236.68   $236.70   $236.70  
  Purchase #2 $171.67   5.848%   $181.7093   $181.71   $181.70   $181.70  
  Purchase #3 $198.79   7.199%   $213.1009   $213.10   $213.10   $213.10  
  Purchase #4 $53.45   7.829%   $57.6346   $57.63   $57.65   $57.60  
  Purchase #5 $132.52   11.315%   $147.5146   $147.51   $147.50   $147.50  
  Purchase #6 $73.67   9.550%   $80.7055   $80.71   $80.70   $80.70  
  Purchase #7 $51.79   4.566%   $54.1547   $54.15   $54.15   $54.20  
  7 purchase totals = $901.55       $971.5033   $971.49   $971.50   $971.50