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 $70.82   8.743%   $77.0118   $77.01   $77.00   $77.00  
  Purchase #2 $81.62   13.867%   $92.9382   $92.94   $92.95   $92.90  
  Purchase #3 $167.51   8.624%   $181.9561   $181.96   $181.95   $182.00  
  Purchase #4 $67.65   11.763%   $75.6077   $75.61   $75.60   $75.60  
  Purchase #5 $177.28   5.700%   $187.385   $187.39   $187.40   $187.40  
  Purchase #6 $205.33   4.577%   $214.728   $214.73   $214.75   $214.70  
  Purchase #7 $22.65   6.839%   $24.199   $24.20   $24.20   $24.20  
  7 purchase totals = $792.86       $853.8258   $853.84   $853.85   $853.80