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 $106.41   9.228%   $116.2295   $116.23   $116.25   $116.20  
  Purchase #2 $133.43   12.363%   $149.926   $149.93   $149.95   $149.90  
  Purchase #3 $72.94   10.344%   $80.4849   $80.48   $80.50   $80.50  
  Purchase #4 $165.94   7.638%   $178.6145   $178.61   $178.60   $178.60  
  Purchase #5 $90.74   5.816%   $96.0174   $96.02   $96.00   $96.00  
  Purchase #6 $145.38   11.227%   $161.7018   $161.70   $161.70   $161.70  
  Purchase #7 $60.29   7.326%   $64.7068   $64.71   $64.70   $64.70  
  7 purchase totals = $775.13       $847.6809   $847.68   $847.70   $847.60