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 $58.99   4.763%   $61.7997   $61.80   $61.80   $61.80  
  Purchase #2 $234.60   3.245%   $242.2128   $242.21   $242.20   $242.20  
  Purchase #3 $72.50   4.592%   $75.8292   $75.83   $75.85   $75.80  
  Purchase #4 $100.79   7.151%   $107.9975   $108.00   $108.00   $108.00  
  Purchase #5 $128.36   9.132%   $140.0818   $140.08   $140.10   $140.10  
  Purchase #6 $182.60   6.763%   $194.9492   $194.95   $194.95   $194.90  
  Purchase #7 $180.70   12.630%   $203.5224   $203.52   $203.50   $203.50  
  7 purchase totals = $958.54       $1,026.3926   $1,026.39   $1,026.40   $1,026.30