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 $191.79   6.791%   $204.8145   $204.81   $204.80   $204.80  
  Purchase #2 $106.93   11.615%   $119.3499   $119.35   $119.35   $119.30  
  Purchase #3 $234.43   12.633%   $264.0455   $264.05   $264.05   $264.00  
  Purchase #4 $60.73   12.471%   $68.3036   $68.30   $68.30   $68.30  
  Purchase #5 $149.52   10.274%   $164.8817   $164.88   $164.90   $164.90  
  Purchase #6 $212.48   13.838%   $241.883   $241.88   $241.90   $241.90  
  Purchase #7 $139.76   3.791%   $145.0583   $145.06   $145.05   $145.10  
  7 purchase totals = $1,095.64       $1,208.3365   $1,208.33   $1,208.35   $1,208.30