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 $193.91   7.114%   $207.7048   $207.70   $207.70   $207.70  
  Purchase #2 $246.96   12.159%   $276.9879   $276.99   $277.00   $277.00  
  Purchase #3 $119.80   5.782%   $126.7268   $126.73   $126.75   $126.70  
  Purchase #4 $33.94   9.344%   $37.1114   $37.11   $37.10   $37.10  
  Purchase #5 $238.52   4.550%   $249.3727   $249.37   $249.35   $249.40  
  Purchase #6 $203.56   3.720%   $211.1324   $211.13   $211.15   $211.10  
  Purchase #7 $14.92   5.836%   $15.7907   $15.79   $15.80   $15.80  
  7 purchase totals = $1,051.61       $1,124.8267   $1,124.82   $1,124.85   $1,124.80