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 $63.73   6.632%   $67.9566   $67.96   $67.95   $68.00  
  Purchase #2 $135.43   8.282%   $146.6463   $146.65   $146.65   $146.60  
  Purchase #3 $203.29   8.640%   $220.8543   $220.85   $220.85   $220.90  
  Purchase #4 $129.46   12.297%   $145.3797   $145.38   $145.40   $145.40  
  Purchase #5 $94.72   4.499%   $98.9815   $98.98   $99.00   $99.00  
  Purchase #6 $176.42   10.824%   $195.5157   $195.52   $195.50   $195.50  
  Purchase #7 $159.70   6.326%   $169.8026   $169.80   $169.80   $169.80  
  7 purchase totals = $962.75       $1,045.1367   $1,045.14   $1,045.15   $1,045.20