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 $54.33   13.814%   $61.8351   $61.84   $61.85   $61.80  
  Purchase #2 $110.54   8.227%   $119.6341   $119.63   $119.65   $119.60  
  Purchase #3 $230.96   6.533%   $246.0486   $246.05   $246.05   $246.00  
  Purchase #4 $202.35   6.241%   $214.9787   $214.98   $215.00   $215.00  
  Purchase #5 $68.32   12.692%   $76.9912   $76.99   $77.00   $77.00  
  Purchase #6 $75.94   3.124%   $78.3124   $78.31   $78.30   $78.30  
  Purchase #7 $181.54   12.835%   $204.8407   $204.84   $204.85   $204.80  
  7 purchase totals = $923.98       $1,002.6408   $1,002.64   $1,002.70   $1,002.50