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 $83.74   10.270%   $92.3401   $92.34   $92.35   $92.30  
  Purchase #2 $74.40   9.483%   $81.4554   $81.46   $81.45   $81.50  
  Purchase #3 $212.64   9.561%   $232.9705   $232.97   $232.95   $233.00  
  Purchase #4 $62.49   9.669%   $68.5322   $68.53   $68.55   $68.50  
  Purchase #5 $36.37   12.760%   $41.0108   $41.01   $41.00   $41.00  
  Purchase #6 $105.47   3.755%   $109.4304   $109.43   $109.45   $109.40  
  Purchase #7 $128.45   9.127%   $140.1736   $140.17   $140.15   $140.20  
  7 purchase totals = $703.56       $765.9130   $765.91   $765.90   $765.90