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 $173.59   8.557%   $188.4441   $188.44   $188.45   $188.40  
  Purchase #2 $67.56   8.169%   $73.079   $73.08   $73.10   $73.10  
  Purchase #3 $44.52   7.340%   $47.7878   $47.79   $47.80   $47.80  
  Purchase #4 $5.29   6.315%   $5.6241   $5.62   $5.60   $5.60  
  Purchase #5 $80.73   7.841%   $87.06   $87.06   $87.05   $87.10  
  Purchase #6 $203.52   3.466%   $210.574   $210.57   $210.55   $210.60  
  Purchase #7 $236.46   8.493%   $256.5425   $256.54   $256.55   $256.50  
  7 purchase totals = $811.67       $869.1115   $869.10   $869.10   $869.10