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 $181.97   12.287%   $204.3287   $204.33   $204.35   $204.30  
  Purchase #2 $181.25   11.223%   $201.5917   $201.59   $201.60   $201.60  
  Purchase #3 $203.42   6.348%   $216.3331   $216.33   $216.35   $216.30  
  Purchase #4 $87.70   5.331%   $92.3753   $92.38   $92.40   $92.40  
  Purchase #5 $81.88   10.477%   $90.4586   $90.46   $90.45   $90.50  
  Purchase #6 $24.45   10.453%   $27.0058   $27.01   $27.00   $27.00  
  Purchase #7 $84.44   11.298%   $93.98   $93.98   $94.00   $94.00  
  7 purchase totals = $845.11       $926.0732   $926.08   $926.15   $926.10