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 $84.40   4.676%   $88.3465   $88.35   $88.35   $88.30  
  Purchase #2 $156.72   8.344%   $169.7967   $169.80   $169.80   $169.80  
  Purchase #3 $181.56   10.130%   $199.952   $199.95   $199.95   $200.00  
  Purchase #4 $197.85   5.757%   $209.2402   $209.24   $209.25   $209.20  
  Purchase #5 $150.55   6.506%   $160.3448   $160.34   $160.35   $160.30  
  Purchase #6 $80.68   12.115%   $90.4544   $90.45   $90.45   $90.50  
  Purchase #7 $97.28   11.745%   $108.7055   $108.71   $108.70   $108.70  
  7 purchase totals = $949.04       $1,026.8401   $1,026.84   $1,026.85   $1,026.80