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 $197.92   12.674%   $223.0044   $223.00   $223.00   $223.00  
  Purchase #2 $22.62   10.782%   $25.0589   $25.06   $25.05   $25.10  
  Purchase #3 $64.93   10.842%   $71.9697   $71.97   $71.95   $72.00  
  Purchase #4 $80.56   9.748%   $88.413   $88.41   $88.40   $88.40  
  Purchase #5 $209.39   5.494%   $220.8939   $220.89   $220.90   $220.90  
  Purchase #6 $174.91   3.619%   $181.24   $181.24   $181.25   $181.20  
  Purchase #7 $121.76   10.300%   $134.3013   $134.30   $134.30   $134.30  
  7 purchase totals = $872.09       $944.8812   $944.87   $944.85   $944.90