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 $212.53   12.185%   $238.4268   $238.43   $238.45   $238.40  
  Purchase #2 $240.96   13.629%   $273.8004   $273.80   $273.80   $273.80  
  Purchase #3 $249.82   7.289%   $268.0294   $268.03   $268.05   $268.00  
  Purchase #4 $56.59   9.334%   $61.8721   $61.87   $61.85   $61.90  
  Purchase #5 $129.53   12.238%   $145.3819   $145.38   $145.40   $145.40  
  Purchase #6 $74.53   11.866%   $83.3737   $83.37   $83.35   $83.40  
  Purchase #7 $22.26   5.664%   $23.5208   $23.52   $23.50   $23.50  
  7 purchase totals = $986.22       $1,094.4051   $1,094.40   $1,094.40   $1,094.40