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 $74.58   6.272%   $79.2577   $79.26   $79.25   $79.30  
  Purchase #2 $181.96   11.787%   $203.4076   $203.41   $203.40   $203.40  
  Purchase #3 $78.77   7.463%   $84.6486   $84.65   $84.65   $84.60  
  Purchase #4 $183.52   10.389%   $202.5859   $202.59   $202.60   $202.60  
  Purchase #5 $146.61   7.307%   $157.3228   $157.32   $157.30   $157.30  
  Purchase #6 $97.75   13.843%   $111.2815   $111.28   $111.30   $111.30  
  Purchase #7 $163.99   5.701%   $173.3391   $173.34   $173.35   $173.30  
  7 purchase totals = $927.18       $1,011.8432   $1,011.85   $1,011.85   $1,011.80