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 $144.59   6.287%   $153.6804   $153.68   $153.70   $153.70  
  Purchase #2 $91.50   11.839%   $102.3327   $102.33   $102.35   $102.30  
  Purchase #3 $145.58   3.541%   $150.735   $150.74   $150.75   $150.70  
  Purchase #4 $198.25   9.581%   $217.2443   $217.24   $217.25   $217.20  
  Purchase #5 $25.55   4.686%   $26.7473   $26.75   $26.75   $26.70  
  Purchase #6 $221.58   9.701%   $243.0755   $243.08   $243.10   $243.10  
  Purchase #7 $159.50   6.315%   $169.5724   $169.57   $169.55   $169.60  
  7 purchase totals = $986.55       $1,063.3876   $1,063.39   $1,063.45   $1,063.30