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 $36.83   3.221%   $38.0163   $38.02   $38.00   $38.00  
  Purchase #2 $138.57   4.376%   $144.6338   $144.63   $144.65   $144.60  
  Purchase #3 $197.90   3.435%   $204.6979   $204.70   $204.70   $204.70  
  Purchase #4 $249.29   9.629%   $273.2941   $273.29   $273.30   $273.30  
  Purchase #5 $156.87   13.667%   $178.3094   $178.31   $178.30   $178.30  
  Purchase #6 $100.67   5.837%   $106.5461   $106.55   $106.55   $106.50  
  Purchase #7 $70.65   4.541%   $73.8582   $73.86   $73.85   $73.90  
  7 purchase totals = $950.78       $1,019.3558   $1,019.36   $1,019.35   $1,019.30