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 $62.47   5.670%   $66.012   $66.01   $66.00   $66.00  
  Purchase #2 $184.55   12.208%   $207.0799   $207.08   $207.10   $207.10  
  Purchase #3 $23.33   3.758%   $24.2067   $24.21   $24.20   $24.20  
  Purchase #4 $87.75   7.421%   $94.2619   $94.26   $94.25   $94.30  
  Purchase #5 $90.46   6.194%   $96.0631   $96.06   $96.05   $96.10  
  Purchase #6 $244.33   6.771%   $260.8736   $260.87   $260.85   $260.90  
  Purchase #7 $238.33   6.675%   $254.2385   $254.24   $254.25   $254.20  
  7 purchase totals = $931.22       $1,002.7357   $1,002.73   $1,002.70   $1,002.80