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 $183.98   10.143%   $202.6411   $202.64   $202.65   $202.60  
  Purchase #2 $137.74   11.453%   $153.5154   $153.52   $153.50   $153.50  
  Purchase #3 $54.61   5.841%   $57.7998   $57.80   $57.80   $57.80  
  Purchase #4 $115.80   9.276%   $126.5416   $126.54   $126.55   $126.50  
  Purchase #5 $6.52   3.320%   $6.7365   $6.74   $6.75   $6.70  
  Purchase #6 $194.70   8.450%   $211.1522   $211.15   $211.15   $211.20  
  Purchase #7 $105.99   10.170%   $116.7692   $116.77   $116.75   $116.80  
  7 purchase totals = $799.34       $875.1558   $875.16   $875.15   $875.10