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 $64.57   5.298%   $67.9909   $67.99   $68.00   $68.00  
  Purchase #2 $32.72   11.823%   $36.5885   $36.59   $36.60   $36.60  
  Purchase #3 $85.50   6.632%   $91.1704   $91.17   $91.15   $91.20  
  Purchase #4 $169.86   12.589%   $191.2437   $191.24   $191.25   $191.20  
  Purchase #5 $10.86   5.567%   $11.4646   $11.46   $11.45   $11.50  
  Purchase #6 $172.34   5.192%   $181.2879   $181.29   $181.30   $181.30  
  Purchase #7 $32.34   6.214%   $34.3496   $34.35   $34.35   $34.30  
  7 purchase totals = $568.19       $614.0956   $614.09   $614.10   $614.10