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 $15.45   12.570%   $17.3921   $17.39   $17.40   $17.40  
  Purchase #2 $81.44   11.837%   $91.0801   $91.08   $91.10   $91.10  
  Purchase #3 $223.69   9.751%   $245.502   $245.50   $245.50   $245.50  
  Purchase #4 $232.47   4.592%   $243.145   $243.15   $243.15   $243.10  
  Purchase #5 $155.65   8.415%   $168.7479   $168.75   $168.75   $168.70  
  Purchase #6 $187.93   3.788%   $195.0488   $195.05   $195.05   $195.00  
  Purchase #7 $197.26   9.194%   $215.3961   $215.40   $215.40   $215.40  
  7 purchase totals = $1,093.89       $1,176.3120   $1,176.32   $1,176.35   $1,176.20