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 $180.60   12.472%   $203.1244   $203.12   $203.10   $203.10  
  Purchase #2 $101.64   13.303%   $115.1612   $115.16   $115.15   $115.20  
  Purchase #3 $223.57   3.768%   $231.9941   $231.99   $232.00   $232.00  
  Purchase #4 $22.78   5.684%   $24.0748   $24.07   $24.05   $24.10  
  Purchase #5 $65.84   12.339%   $73.964   $73.96   $73.95   $74.00  
  Purchase #6 $183.47   4.278%   $191.3188   $191.32   $191.30   $191.30  
  Purchase #7 $162.39   7.702%   $174.8973   $174.90   $174.90   $174.90  
  7 purchase totals = $940.29       $1,014.5346   $1,014.52   $1,014.45   $1,014.60