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 $92.98   5.227%   $97.8401   $97.84   $97.85   $97.80  
  Purchase #2 $156.47   6.206%   $166.1805   $166.18   $166.20   $166.20  
  Purchase #3 $232.90   4.716%   $243.8836   $243.88   $243.90   $243.90  
  Purchase #4 $169.52   4.738%   $177.5519   $177.55   $177.55   $177.60  
  Purchase #5 $192.33   13.529%   $218.3503   $218.35   $218.35   $218.40  
  Purchase #6 $113.47   5.755%   $120.0002   $120.00   $120.00   $120.00  
  Purchase #7 $85.29   12.704%   $96.1252   $96.13   $96.15   $96.10  
  7 purchase totals = $1,042.96       $1,119.9318   $1,119.93   $1,120.00   $1,120.00