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 $202.66   4.216%   $211.2041   $211.20   $211.20   $211.20  
  Purchase #2 $223.81   10.343%   $246.9587   $246.96   $246.95   $247.00  
  Purchase #3 $123.63   8.108%   $133.6539   $133.65   $133.65   $133.70  
  Purchase #4 $137.27   13.565%   $155.8907   $155.89   $155.90   $155.90  
  Purchase #5 $165.93   8.713%   $180.3875   $180.39   $180.40   $180.40  
  Purchase #6 $205.60   3.151%   $212.0785   $212.08   $212.10   $212.10  
  Purchase #7 $82.78   3.638%   $85.7915   $85.79   $85.80   $85.80  
  7 purchase totals = $1,141.68       $1,225.9649   $1,225.96   $1,226.00   $1,226.10