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 $7.87   12.135%   $8.825   $8.83   $8.85   $8.80  
  Purchase #2 $173.96   3.700%   $180.3965   $180.40   $180.40   $180.40  
  Purchase #3 $182.47   3.654%   $189.1375   $189.14   $189.15   $189.10  
  Purchase #4 $222.89   12.708%   $251.2149   $251.21   $251.20   $251.20  
  Purchase #5 $113.35   5.621%   $119.7214   $119.72   $119.70   $119.70  
  Purchase #6 $215.52   5.827%   $228.0784   $228.08   $228.10   $228.10  
  Purchase #7 $120.82   9.600%   $132.4187   $132.42   $132.40   $132.40  
  7 purchase totals = $1,036.88       $1,109.7924   $1,109.80   $1,109.80   $1,109.70