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 $171.39   13.781%   $195.0093   $195.01   $195.00   $195.00  
  Purchase #2 $99.85   4.494%   $104.3373   $104.34   $104.35   $104.30  
  Purchase #3 $54.95   8.313%   $59.518   $59.52   $59.50   $59.50  
  Purchase #4 $39.70   10.235%   $43.7633   $43.76   $43.75   $43.80  
  Purchase #5 $38.55   7.574%   $41.4698   $41.47   $41.45   $41.50  
  Purchase #6 $138.57   13.730%   $157.5957   $157.60   $157.60   $157.60  
  Purchase #7 $234.86   7.562%   $252.6201   $252.62   $252.60   $252.60  
  7 purchase totals = $777.87       $854.3135   $854.32   $854.25   $854.30