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 $117.74   3.658%   $122.0469   $122.05   $122.05   $122.00  
  Purchase #2 $176.64   9.141%   $192.7867   $192.79   $192.80   $192.80  
  Purchase #3 $144.80   4.259%   $150.967   $150.97   $150.95   $151.00  
  Purchase #4 $230.83   10.375%   $254.7786   $254.78   $254.80   $254.80  
  Purchase #5 $95.34   7.378%   $102.3742   $102.37   $102.35   $102.40  
  Purchase #6 $218.39   11.533%   $243.5769   $243.58   $243.60   $243.60  
  Purchase #7 $11.58   10.758%   $12.8258   $12.83   $12.85   $12.80  
  7 purchase totals = $995.32       $1,079.3561   $1,079.37   $1,079.40   $1,079.40