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 $155.37   13.473%   $176.303   $176.30   $176.30   $176.30  
  Purchase #2 $59.42   5.573%   $62.7315   $62.73   $62.75   $62.70  
  Purchase #3 $85.80   6.306%   $91.2105   $91.21   $91.20   $91.20  
  Purchase #4 $129.88   4.392%   $135.5843   $135.58   $135.60   $135.60  
  Purchase #5 $200.89   9.764%   $220.5049   $220.50   $220.50   $220.50  
  Purchase #6 $163.38   11.531%   $182.2193   $182.22   $182.20   $182.20  
  Purchase #7 $220.79   5.123%   $232.1011   $232.10   $232.10   $232.10  
  7 purchase totals = $1,015.53       $1,100.6546   $1,100.64   $1,100.65   $1,100.60