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 $128.51   6.624%   $137.0225   $137.02   $137.00   $137.00  
  Purchase #2 $216.79   13.172%   $245.3456   $245.35   $245.35   $245.30  
  Purchase #3 $247.93   9.235%   $270.8263   $270.83   $270.85   $270.80  
  Purchase #4 $101.73   11.637%   $113.5683   $113.57   $113.55   $113.60  
  Purchase #5 $72.73   12.503%   $81.8234   $81.82   $81.80   $81.80  
  Purchase #6 $218.46   13.620%   $248.2143   $248.21   $248.20   $248.20  
  Purchase #7 $99.96   6.377%   $106.3344   $106.33   $106.35   $106.30  
  7 purchase totals = $1,086.11       $1,203.1348   $1,203.13   $1,203.10   $1,203.00