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 $204.33   12.455%   $229.7793   $229.78   $229.80   $229.80  
  Purchase #2 $114.69   11.344%   $127.7004   $127.70   $127.70   $127.70  
  Purchase #3 $160.72   11.765%   $179.6287   $179.63   $179.65   $179.60  
  Purchase #4 $52.96   13.809%   $60.2732   $60.27   $60.25   $60.30  
  Purchase #5 $247.30   5.387%   $260.6221   $260.62   $260.60   $260.60  
  Purchase #6 $92.86   4.523%   $97.0601   $97.06   $97.05   $97.10  
  Purchase #7 $108.60   11.465%   $121.051   $121.05   $121.05   $121.10  
  7 purchase totals = $981.46       $1,076.1148   $1,076.11   $1,076.10   $1,076.20