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 $50.37   12.360%   $56.5957   $56.60   $56.60   $56.60  
  Purchase #2 $234.56   13.597%   $266.4531   $266.45   $266.45   $266.50  
  Purchase #3 $149.72   8.571%   $162.5525   $162.55   $162.55   $162.60  
  Purchase #4 $232.72   5.207%   $244.8377   $244.84   $244.85   $244.80  
  Purchase #5 $189.84   6.377%   $201.9461   $201.95   $201.95   $201.90  
  Purchase #6 $135.60   11.132%   $150.695   $150.70   $150.70   $150.70  
  Purchase #7 $33.98   7.575%   $36.554   $36.55   $36.55   $36.60  
  7 purchase totals = $1,026.79       $1,119.6341   $1,119.64   $1,119.65   $1,119.70