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 $176.98   11.662%   $197.6194   $197.62   $197.60   $197.60  
  Purchase #2 $156.29   6.415%   $166.316   $166.32   $166.30   $166.30  
  Purchase #3 $38.46   8.402%   $41.6914   $41.69   $41.70   $41.70  
  Purchase #4 $49.27   7.768%   $53.0973   $53.10   $53.10   $53.10  
  Purchase #5 $209.52   10.661%   $231.8569   $231.86   $231.85   $231.90  
  Purchase #6 $64.70   7.761%   $69.7214   $69.72   $69.70   $69.70  
  Purchase #7 $214.67   8.498%   $232.9127   $232.91   $232.90   $232.90  
  7 purchase totals = $909.89       $993.2151   $993.22   $993.15   $993.20