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 $6.41   12.118%   $7.1868   $7.19   $7.20   $7.20  
  Purchase #2 $219.93   12.397%   $247.1947   $247.19   $247.20   $247.20  
  Purchase #3 $84.84   10.854%   $94.0485   $94.05   $94.05   $94.00  
  Purchase #4 $60.43   3.242%   $62.3891   $62.39   $62.40   $62.40  
  Purchase #5 $110.41   9.780%   $121.2081   $121.21   $121.20   $121.20  
  Purchase #6 $211.40   12.375%   $237.5608   $237.56   $237.55   $237.60  
  Purchase #7 $10.52   10.415%   $11.6157   $11.62   $11.60   $11.60  
  7 purchase totals = $703.94       $781.2037   $781.21   $781.20   $781.20