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 $90.82   6.861%   $97.0512   $97.05   $97.05   $97.10  
  Purchase #2 $138.92   8.146%   $150.2364   $150.24   $150.25   $150.20  
  Purchase #3 $191.89   7.107%   $205.5276   $205.53   $205.55   $205.50  
  Purchase #4 $244.64   7.421%   $262.7947   $262.79   $262.80   $262.80  
  Purchase #5 $174.94   9.493%   $191.5471   $191.55   $191.55   $191.50  
  Purchase #6 $186.53   5.816%   $197.3786   $197.38   $197.40   $197.40  
  Purchase #7 $7.96   3.573%   $8.2444   $8.24   $8.25   $8.20  
  7 purchase totals = $1,035.70       $1,112.7800   $1,112.78   $1,112.85   $1,112.70