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 $143.77   5.350%   $151.4617   $151.46   $151.45   $151.50  
  Purchase #2 $159.47   10.364%   $175.9975   $176.00   $176.00   $176.00  
  Purchase #3 $224.40   6.803%   $239.6659   $239.67   $239.65   $239.70  
  Purchase #4 $88.46   12.455%   $99.4777   $99.48   $99.50   $99.50  
  Purchase #5 $93.54   9.560%   $102.4824   $102.48   $102.50   $102.50  
  Purchase #6 $214.40   13.706%   $243.7857   $243.79   $243.80   $243.80  
  Purchase #7 $11.53   4.367%   $12.0335   $12.03   $12.05   $12.00  
  7 purchase totals = $935.57       $1,024.9044   $1,024.91   $1,024.95   $1,025.00