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 $81.87   12.509%   $92.1111   $92.11   $92.10   $92.10  
  Purchase #2 $232.40   4.843%   $243.6551   $243.66   $243.65   $243.70  
  Purchase #3 $87.31   9.404%   $95.5206   $95.52   $95.50   $95.50  
  Purchase #4 $218.73   9.272%   $239.0106   $239.01   $239.00   $239.00  
  Purchase #5 $38.82   4.228%   $40.4613   $40.46   $40.45   $40.50  
  Purchase #6 $109.35   6.626%   $116.5955   $116.60   $116.60   $116.60  
  Purchase #7 $37.47   11.232%   $41.6786   $41.68   $41.70   $41.70  
  7 purchase totals = $805.95       $869.0328   $869.04   $869.00   $869.10