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 $202.29   11.726%   $226.0105   $226.01   $226.00   $226.00  
  Purchase #2 $235.42   12.124%   $263.9623   $263.96   $263.95   $264.00  
  Purchase #3 $42.51   7.673%   $45.7718   $45.77   $45.75   $45.80  
  Purchase #4 $203.39   9.250%   $222.2036   $222.20   $222.20   $222.20  
  Purchase #5 $22.34   7.338%   $23.9793   $23.98   $24.00   $24.00  
  Purchase #6 $89.99   7.748%   $96.9624   $96.96   $96.95   $97.00  
  Purchase #7 $49.53   7.607%   $53.2977   $53.30   $53.30   $53.30  
  7 purchase totals = $845.47       $932.1876   $932.18   $932.15   $932.30