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 $107.57   10.654%   $119.0305   $119.03   $119.05   $119.00  
  Purchase #2 $226.51   12.332%   $254.4432   $254.44   $254.45   $254.40  
  Purchase #3 $136.64   9.314%   $149.3666   $149.37   $149.35   $149.40  
  Purchase #4 $115.46   13.550%   $131.1048   $131.10   $131.10   $131.10  
  Purchase #5 $9.37   6.344%   $9.9644   $9.96   $9.95   $10.00  
  Purchase #6 $32.85   13.558%   $37.3038   $37.30   $37.30   $37.30  
  Purchase #7 $150.30   7.206%   $161.1306   $161.13   $161.15   $161.10  
  7 purchase totals = $778.70       $862.3439   $862.33   $862.35   $862.30