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 $79.53   6.822%   $84.9555   $84.96   $84.95   $85.00  
  Purchase #2 $197.43   6.716%   $210.6894   $210.69   $210.70   $210.70  
  Purchase #3 $169.33   4.690%   $177.2716   $177.27   $177.25   $177.30  
  Purchase #4 $188.87   8.375%   $204.6879   $204.69   $204.70   $204.70  
  Purchase #5 $123.86   11.557%   $138.1745   $138.17   $138.15   $138.20  
  Purchase #6 $124.25   4.242%   $129.5207   $129.52   $129.50   $129.50  
  Purchase #7 $92.40   4.272%   $96.3473   $96.35   $96.35   $96.30  
  7 purchase totals = $975.67       $1,041.6469   $1,041.65   $1,041.60   $1,041.70