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 $44.79   8.452%   $48.5757   $48.58   $48.60   $48.60  
  Purchase #2 $49.80   6.199%   $52.8871   $52.89   $52.90   $52.90  
  Purchase #3 $245.29   12.604%   $276.2064   $276.21   $276.20   $276.20  
  Purchase #4 $107.84   13.460%   $122.3553   $122.36   $122.35   $122.40  
  Purchase #5 $203.90   9.460%   $223.1889   $223.19   $223.20   $223.20  
  Purchase #6 $169.41   3.278%   $174.9633   $174.96   $174.95   $175.00  
  Purchase #7 $159.61   5.384%   $168.2034   $168.20   $168.20   $168.20  
  7 purchase totals = $980.64       $1,066.3801   $1,066.39   $1,066.40   $1,066.50