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 $228.85   11.210%   $254.5041   $254.50   $254.50   $254.50  
  Purchase #2 $65.59   4.340%   $68.4366   $68.44   $68.45   $68.40  
  Purchase #3 $32.57   12.467%   $36.6305   $36.63   $36.65   $36.60  
  Purchase #4 $241.48   6.437%   $257.0241   $257.02   $257.00   $257.00  
  Purchase #5 $245.91   13.312%   $278.6455   $278.65   $278.65   $278.60  
  Purchase #6 $90.34   6.780%   $96.4651   $96.47   $96.45   $96.50  
  Purchase #7 $92.30   11.309%   $102.7382   $102.74   $102.75   $102.70  
  7 purchase totals = $997.04       $1,094.4441   $1,094.45   $1,094.45   $1,094.30