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 $169.79   12.813%   $191.5452   $191.55   $191.55   $191.50  
  Purchase #2 $243.98   11.618%   $272.3256   $272.33   $272.35   $272.30  
  Purchase #3 $32.52   10.202%   $35.8377   $35.84   $35.85   $35.80  
  Purchase #4 $171.65   6.829%   $183.372   $183.37   $183.35   $183.40  
  Purchase #5 $249.56   7.722%   $268.831   $268.83   $268.85   $268.80  
  Purchase #6 $230.41   4.527%   $240.8407   $240.84   $240.85   $240.80  
  Purchase #7 $180.29   6.417%   $191.8592   $191.86   $191.85   $191.90  
  7 purchase totals = $1,278.20       $1,384.6114   $1,384.62   $1,384.65   $1,384.50