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 $183.52   9.629%   $201.1911   $201.19   $201.20   $201.20  
  Purchase #2 $188.47   6.819%   $201.3218   $201.32   $201.30   $201.30  
  Purchase #3 $244.74   12.249%   $274.7182   $274.72   $274.70   $274.70  
  Purchase #4 $64.42   5.236%   $67.793   $67.79   $67.80   $67.80  
  Purchase #5 $33.39   5.652%   $35.2772   $35.28   $35.30   $35.30  
  Purchase #6 $37.89   6.723%   $40.4373   $40.44   $40.45   $40.40  
  Purchase #7 $160.96   12.864%   $181.6659   $181.67   $181.65   $181.70  
  7 purchase totals = $913.39       $1,002.4045   $1,002.41   $1,002.40   $1,002.40