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 $69.67   10.513%   $76.9944   $76.99   $77.00   $77.00  
  Purchase #2 $159.39   9.283%   $174.1862   $174.19   $174.20   $174.20  
  Purchase #3 $207.71   7.257%   $222.7835   $222.78   $222.80   $222.80  
  Purchase #4 $230.61   9.206%   $251.84   $251.84   $251.85   $251.80  
  Purchase #5 $235.51   9.399%   $257.6456   $257.65   $257.65   $257.60  
  Purchase #6 $65.52   9.637%   $71.8342   $71.83   $71.85   $71.80  
  Purchase #7 $230.42   4.246%   $240.2036   $240.20   $240.20   $240.20  
  7 purchase totals = $1,198.83       $1,295.4875   $1,295.48   $1,295.55   $1,295.40