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 $177.70   13.604%   $201.8743   $201.87   $201.85   $201.90  
  Purchase #2 $228.81   10.370%   $252.5376   $252.54   $252.55   $252.50  
  Purchase #3 $53.51   7.792%   $57.6795   $57.68   $57.70   $57.70  
  Purchase #4 $225.44   8.293%   $244.1357   $244.14   $244.15   $244.10  
  Purchase #5 $29.77   9.869%   $32.708   $32.71   $32.70   $32.70  
  Purchase #6 $211.96   11.236%   $235.7758   $235.78   $235.80   $235.80  
  Purchase #7 $150.26   7.597%   $161.6753   $161.68   $161.70   $161.70  
  7 purchase totals = $1,077.45       $1,186.3862   $1,186.40   $1,186.45   $1,186.40