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 $50.48   12.582%   $56.8314   $56.83   $56.85   $56.80  
  Purchase #2 $97.81   6.194%   $103.8684   $103.87   $103.85   $103.90  
  Purchase #3 $113.96   9.673%   $124.9834   $124.98   $125.00   $125.00  
  Purchase #4 $237.39   11.393%   $264.4358   $264.44   $264.45   $264.40  
  Purchase #5 $189.33   6.374%   $201.3979   $201.40   $201.40   $201.40  
  Purchase #6 $37.92   3.547%   $39.265   $39.27   $39.25   $39.30  
  Purchase #7 $47.56   13.576%   $54.0167   $54.02   $54.00   $54.00  
  7 purchase totals = $774.45       $844.7986   $844.81   $844.80   $844.80