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 $113.46   8.646%   $123.2698   $123.27   $123.25   $123.30  
  Purchase #2 $10.77   7.400%   $11.567   $11.57   $11.55   $11.60  
  Purchase #3 $146.81   8.654%   $159.5149   $159.51   $159.50   $159.50  
  Purchase #4 $187.52   9.319%   $204.995   $205.00   $205.00   $205.00  
  Purchase #5 $134.28   7.344%   $144.1415   $144.14   $144.15   $144.10  
  Purchase #6 $160.81   3.217%   $165.9833   $165.98   $166.00   $166.00  
  Purchase #7 $228.25   10.179%   $251.4836   $251.48   $251.50   $251.50  
  7 purchase totals = $981.90       $1,060.9551   $1,060.95   $1,060.95   $1,061.00